Method for transmitting a sidelink buffer status reporting in a d2d communication system and device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for transmitting a sidelink buffer status reporting in a D2D communication system, the method comprising: transmitting information related to a first destination information list including at least one groupcast destination ID and a second destination information list including at least one unicast destination ID; assigning values of destination index for groupcast to groupcast destinations IDs in listing order in the first destination information list and values of destination index for unicast to unicast destinations IDs in listing order in the second destination information list; and generating and transmitting a SL BSR MAC CE including at least one index type indication indicating whether a corresponding destination index field refers to a unicast destination or a groupcast destination, when SL BSR is triggered.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for transmitting a sidelink buffer statusreporting in a D2D (Device to Device) communication system and a devicetherefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARQ)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Device to device (D2D) communication refers to the distributedcommunication technology that directly transfers traffic betweenadjacent nodes without using infrastructure such as a base station. In aD2D communication environment, each node such as a portable terminaldiscovers user equipment physically adjacent thereto and transmitstraffic after setting communication session. In this way, since D2Dcommunication may solve traffic overload by distributing trafficconcentrated into the base station, the D2D communication may havereceived attention as the element technology of the next generationmobile communication technology after 4G. For this reason, the standardinstitute such as 3GPP or IEEE has proceeded to establish the D2Dcommunication standard on the basis of LTE-A or Wi-Fi, and Qualcomm hasdeveloped their own D2D communication technology.

It is expected that the D2D communication contributes to increasethroughput of a mobile communication system and create new communicationservices. Also, the D2D communication may support proximity based socialnetwork services or network game services. The problem of link of a userequipment located at a shade zone may be solved by using a D2D link as arelay. In this way, it is expected that the D2D technology will providenew services in various fields.

The D2D communication technologies such as infrared communication,ZigBee, radio frequency identification (RFID) and near fieldcommunications (NFC) based on the RFID have been already used. However,since these technologies support communication only of a specific objectwithin a limited distance (about 1 m), it is difficult for thetechnologies to be regarded as the D2D communication technologiesstrictly.

Although the D2D communication has been described as above, details of amethod for transmitting data from a plurality of D2D user equipmentswith the same resource have not been suggested.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method and device for transmitting a sidelink buffer status reportingin a D2D communication system. The technical problems solved by thepresent invention are not limited to the above technical problems andthose skilled in the art may understand other technical problems fromthe following description.

Technical Solution

The object of the present invention can be achieved by providing amethod for User Equipment (UE) operating in a wireless communicationsystem as set forth in the appended claims.

In another aspect of the present invention, provided herein is acommunication apparatus as set forth in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

It is invented that for SL BSR trigger, the UE generates SL BSR MAC CEincluding groupcast information and unicast information.

It will be appreciated by persons skilled in the art that that theeffects achieved by the present invention are not limited to what hasbeen particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a diagram of an example physical channel structure used in anE-UMTS system;

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention

FIG. 6 is an example of default data path for a normal communication;

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication;

FIG. 9 is a conceptual diagram illustrating for a Layer 2 Structure forSidelink;

FIG. 10A is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 10B is Control-Planeprotocol stack for ProSe Direct Communication;

FIG. 11 is an example for PC5 interface between remote UEs and a relayUE; and

FIG. 12 is a diagram for MAC structure overview in a UE side;

FIG. 13A is an example for Sidelink BSR and Truncated Sidelink BSR MACcontrol element for even N, and FIG. 13B is an example for Sidelink BSRand Truncated Sidelink BSR MAC control element for odd N;

FIG. 14 is a diagram for generating and transmitting a sidelink bufferstatus reporting in a D2D communication system according to embodimentsof the present invention;

FIG. 15 is an example for a new SL BSR MAC CE format in a D2Dcommunication system according to embodiments of the present invention;

FIG. 16 is a diagram for generating and transmitting a sidelink bufferstatus reporting in a D2D communication system according to embodimentsof the present invention; and

FIG. 17 is an example for a new SL BSR MAC CE format in a D2Dcommunication system according to embodiments of the present invention.

BEST MODE

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an Si interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNodeB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel. Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention.

The apparatus shown in FIG. 5 can be a user equipment (UE) and/or eNBadapted to perform the above mechanism, but it can be any apparatus forperforming the same operation.

As shown in FIG. 5, the apparatus may comprises a DSP/microprocessor(110) and RF module (transceiver; 135). The DSP/microprocessor (110) iselectrically connected with the transciver (135) and controls it. Theapparatus may further include power management module (105), battery(155), display (115), keypad (120), SIM card (125), memory device (130),speaker (145) and input device (150), based on its implementation anddesigner's choice.

Specifically, FIG. 5 may represent a UE comprising a receiver (135)configured to receive a request message from a network, and atransmitter (135) configured to transmit the transmission or receptiontiming information to the network. These receiver and the transmittercan constitute the transceiver (135). The UE further comprises aprocessor (110) connected to the transceiver (135: receiver andtransmitter).

Also, FIG. 5 may represent a network apparatus comprising a transmitter(135) configured to transmit a request message to a UE and a receiver(135) configured to receive the transmission or reception timinginformation from the UE. These transmitter and receiver may constitutethe transceiver (135). The network further comprises a processor (110)connected to the transmitter and the receiver. This processor (110) maybe configured to calculate latency based on the transmission orreception timing information.

Recently, Proximity-based Service (ProSe) has been discussed in 3GPP.The ProSe enables different UEs to be connected (directly) each other(after appropriate procedure(s), such as authentication), through eNBonly (but not further through Serving Gateway (SGW)/Packet Data NetworkGateway (PDN-GW, PGW)), or through SGW/PGW. Thus, using the ProSe,device to device direct communication can be provided, and it isexpected that every devices will be connected with ubiquitousconnectivity. Direct communication between devices in a near distancecan lessen the load of network. Recently, proximity-based social networkservices have come to public attention, and new kinds of proximity-basedapplications can be emerged and may create new business market andrevenue. For the first step, public safety and critical communicationare required in the market. Group communication is also one of keycomponents in the public safety system. Required functionalities are:Discovery based on proximity, Direct path communication, and Managementof group communications.

Use cases and scenarios are for example: i) Commercial/social use, ii)Network offloading, iii) Public Safety, iv) Integration of currentinfrastructure services, to assure the consistency of the userexperience including reachability and mobility aspects, and v) PublicSafety, in case of absence of EUTRAN coverage (subject to regionalregulation and operator policy, and limited to specific public-safetydesignated frequency bands and terminals)

FIG. 6 is an example of default data path for communication between twoUEs. With reference to FIG. 6, even when two UEs (e.g., UE1, UE2) inclose proximity communicate with each other, their data path (userplane) goes via the operator network. Thus a typical data path for thecommunication involves eNB(s) and/or Gateway(s) (GW(s)) (e.g., SGW/PGW).

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication. If wireless devices (e.g., UE1, UE2) are in proximity ofeach other, they may be able to use a direct mode data path (FIG. 7) ora locally routed data path (FIG. 8). In the direct mode data path,wireless devices are connected directly each other (after appropriateprocedure(s), such as authentication), without eNB and SGW/PGW. In thelocally routed data path, wireless devices are connected each otherthrough eNB only.

FIG. 9 is a conceptual diagram illustrating for a Layer 2 structure forSidelink.

Sidelink communication is a mode of communication whereby UEs cancommunicate with each other directly over the PC5 interface Thiscommunication mode is supported when the UE is served by E-UTRAN andwhen the UE is outside of E-UTRA coverage. Only those UEs authorized tobe used for public safety operation can perform sidelink communication.

In order to perform synchronization for out of coverage operation UE(s)may act as a synchronization source by transmitting SBCCH and asynchronization signal. SBCCH carries the most essential systeminformation needed to receive other sidelink channels and signals. SBCCHalong with a synchronization signal is transmitted with a fixedperiodicity of 40 ms. When the UE is in network coverage, the contentsof SBCCH are derived from the parameters signalled by the eNB. When theUE is out of coverage, if the UE selects another UE as a synchronizationreference, then the content of SBCCH is derived from the received SBCCH;otherwise UE uses pre-configured parameters. SIB18 provides the resourceinformation for synchronization signal and SBCCH transmission. There aretwo pre-configured subframes every 40 ms for out of coverage operation.UE receives synchronization signal and SBCCH in one subframe andtransmit synchronization signal and SBCCH on another subframe if UEbecomes synchronization source based on defined criterion.

UE performs sidelink communication on subframes defined over theduration of Sidelink Control period. The Sidelink Control period is theperiod over which resources allocated in a cell for sidelink controlinformation and sidelink data transmissions occur. Within the SidelinkControl period the UE sends sidelink control information followed bysidelink data. Sidelink control information indicates a Layer 1 ID andcharacteristics of the transmissions (e.g. MCS, location of theresource(s) over the duration of Sidelink Control period, timingalignment).

The UE performs transmission and reception over Uu and PC5 with thefollowing decreasing priority order:

-   -   Uu transmission/reception (highest priority);    -   PC5 sidelink communication transmission/reception;    -   PC5 sidelink discovery announcement/monitoring (lowest        priority).

FIG. 10A is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 10B is Control-Planeprotocol stack for ProSe Direct Communication.

FIG. 10A shows the protocol stack for the user plane, where PDCP, RLCand MAC sublayers (terminate at the other UE) perform the functionslisted for the user plane (e.g. header compression, HARQretransmissions). The PC5 interface consists of PDCP, RLC, MAC and PHYas shown in FIG. 10A.

User plane details of ProSe Direct Communication: i) there is no HARQfeedback for sidelink communication, ii) RLC UM is used for sidelinkcommunication, iii) RLC UM is used for sidelink communication, iv) areceiving RLC UM entity used for sidelink communication does not need tobe configured prior to reception of the first RLC UMD PDU, and v) ROHCUnidirectional Mode is used for header compression in PDCP for sidelinkcommunication.

A UE may establish multiple logical channels. LCID included within theMAC subheader uniquely identifies a logical channel within the scope ofone Source Layer-2 ID and ProSe Layer-2 Group ID combination. Parametersfor logical channel prioritization are not configured. The Accessstratum (AS) is provided with the PPPP of protocol data unit transmittedover PC5 interface by higher layer. There is a PPPP associated with eachlogical channel.

SL-RNTI is an unique identification used for ProSe Direct CommunicationScheduling.

The Source Layer-2 ID identifies the sender of the data in sidelinkcommunication. The Source Layer-2 ID is 24 bits long and is usedtogether with Destination Layer-2 ID and LCID for identification of theRLC UM entity and PDCP entity in the receiver.

The destination Layer-2 ID identifies the target of the data in sidelinkcommunication. The Destination Layer-2 ID is 24 bits long and is splitin the MAC layer into two bit strings: i) One bit string is the LSB part(8 bits) of Destination Layer-2 ID and forwarded to physical layer asGroup Destination ID. This identifies the target of the intended data insidelink control information and is used for filtering of packets at thephysical layer. And ii) Second bit string is the MSB part (16 bits) ofthe Destination Layer-2 ID and is carried within the MAC header. This isused for filtering of packets at the MAC layer.

No Access Stratum signalling is required for group formation and toconfigure Source Layer-2 ID, Destination Layer-2 ID and GroupDestination ID in the UE. These identities are either provided by higherlayer or derived from identities provided by higher layer. In case ofgroupcast and broadcast, the ProSe UE ID provided by higher layer isused directly as the Source Layer-2 ID and the ProSe Layer-2 Group IDprovided by higher layer is used directly as the Destination Layer-2 IDin the MAC layer. In case of one-to-one communications, higher layerprovides Source Layer-2 ID and Destination Layer-2 ID.

FIG. 10B shows the protocol stack for the control plane.

A UE does not establish and maintain a logical connection to receivingUEs prior to one-to-many a sidelink communication. Higher layerestablish and maintain a logical connection for one-to-one sidelinkcommunication including ProSe UE-to-Network Relay operation.

The Access Stratum protocol stack for SBCCH in the PC5 interfaceconsists of RRC, RLC, MAC and PHY as shown below in FIG. 10B.

The PPPP is a ProSe Per-Packet Priority. The ProSe Per-Packet Priorityis summarized as follows:

i) a single UE shall be able to transmit packets of different prioritieson PC5, ii) the UE upper layers provide to the access stratum a ProSePer Packet Priority from a range of possible values, iii) the ProSe PerPacket Priority is used to support preferential transmission of packetsboth intra-UE and across different UEs, iv) the support of 8 prioritylevels for the ProSe Per Packet Priority should be sufficient, v) theProSe Per Packet Priority applies to all PC5 traffic, and vi) the ProSePer Packet Priority is independent of the layer-2 destination of thetransmission.

From the above summary, it seems that SA2 think ProSe packetprioritization based on PPP is very important and should be supported inPC5 interface in any case. Keeping this observation in mind, we explainhow the LCP procedures should be changed from Rel-12.

FIG. 11 is an example for PC5 interface between remote UEs and a relayUE.

In ProSe, a UE communicates with other UEs directly over PC5 interface.

By introducing a Relay UE for UE-to-NW relay, a remote UE transmits datato an eNB via the Relay UE, and the eNB transmits data to the remote UEvia the Relay UE. I.e., the Relay UE relays data to/from eNB.

As data transfer between the remote UE and the Relay UE is ProSecommunication, the Relay UE is communicating with the remote UE over PC5interface. In the meantime, as data transfer between the Relay UE andthe eNB is a normal uplink/downlink (Uu) communication, the Relay UE iscommunicating with the eNB over Uu interface. This implies that if datahas higher priority in PC5 communication, it should also be higherprioritized in Uu communication.

Over PC5 interface, Per-Packet Priority (PPP), is used to prioritize acertain packet, where the priority is independent with ProSe destinationor ProSe UE. In order to prioritize the packet with higher priority overUu interface as well, the Relay UE needs to know the priority of thepacket so that the Relay UE provides more opportunities of transmissionto the packet with higher priority.

In order to transmit on the SL-SCH, the MAC entity must have a sidelinkgrant. The sidelink grant is selected as follows: if the MAC entity isconfigured to receive a sidelink grant dynamically on the PDCCH and moredata is available in STCH than can be transmitted in the current SCperiod, the MAC entity shall determine a set of subframes in whichtransmission of SCI and transmission of first transport block occurusing the received sidelink grant, consider the received sidelink grantto be a configured sidelink grant occurring in those subframes startingat the beginning of the first available SC Period which starts at least4 subframes after the subframe in which the sidelink grant was received,overwriting a previously configured sidelink grant occurring in the sameSC period, if available, and clear the configured sidelink grant at theend of the corresponding SC Period.

If the MAC entity has a configured sidelink grant occurring in thissubframe, and if the configured sidelink grant corresponds totransmission of SCI, the MAC entity shall, for each subframe, instructthe physical layer to transmit SCI corresponding to the configuredsidelink grant.

If the MAC entity has a configured sidelink grant occurring in thissubframe, and if the configured sidelink grant corresponds totransmission of first transport block, the MAC entity shall deliver theconfigured sidelink grant and the associated HARQ information to theSidelink HARQ Entity for this subframe.

For PDU(s) associated with one SCI, MAC shall consider only logicalchannels with same Source Layer-2 ID-Destination Layer-2 ID pairs.

FIG. 12 is a diagram for MAC structure overview in a UE side.

The MAC layer handles logical-channel multiplexing, hybrid-ARQretransmissions, and uplink and downlink scheduling. It is alsoresponsible for multiplexing/demultiplexing data across multiplecomponent carriers when carrier aggregation is used.

The MAC provides services to the RLC in the form of logical channels. Alogical channel is defined by the type of information it carries and isgenerally classified as a control channel, used for transmission ofcontrol and configuration information necessary for operating an LTEsystem, or as a traffic channel, used for the user data. The set oflogical-channel types specified for LTE includes:

-   -   The Broadcast Control Channel (BCCH), used for transmission of        system information from the network to all terminals in a cell.        Prior to accessing the system, a terminal needs to acquire the        system information to find out how the system is configured and,        in general, how to behave properly within a cell.    -   The Paging Control Channel (PCCH), used for paging of terminals        whose location on a cell level is not known to the network. The        paging message therefore needs to be transmitted in multiple        cells.    -   The Common Control Channel (CCCH), used for transmission of        control information in conjunction with random access.    -   The Dedicated Control Channel (DCCH), used for transmission of        control information to/from a terminal. This channel is used for        individual configuration of terminals such as different handover        messages.    -   The Multicast Control Channel (MCCH), used for transmission of        control information required for reception of the MTCH.    -   The Dedicated Traffic Channel (DTCH), used for transmission of        user data to/from a terminal. This is the logical channel type        used for transmission of all uplink and non-MBSFN downlink user        data.    -   The Multicast Traffic Channel (MTCH), used for downlink        transmission of MBMS services.

To support priority handling, multiple logical channels, where eachlogical channel has its own RLC entity, can be multiplexed into onetransport channel by the MAC layer. At the receiver, the MAC layerhandles the corresponding demultiplexing and forwards the RLC PDUs totheir respective RLC entity for in-sequence delivery and the otherfunctions handled by the RLC. To support the demultiplexing at thereceiver, a MAC is used. To each RLC PDU, there is an associatedsub-header in the MAC header. The sub-header contains the identity ofthe logical channel (LCID) from which the RLC PDU originated and thelength of the PDU in bytes. There is also a flag indicating whether thisis the last sub-header or not. One or several RLC PDUs, together withthe MAC header and, if necessary, padding to meet the scheduledtransport-block size, form one transport block which is forwarded to thephysical layer.

In addition to multiplexing of different logical channels, the MAC layercan also insert the so-called MAC control elements into the transportblocks to be transmitted over the transport channels. A MAC controlelement is used for inband control signaling—for example, timing-advancecommands and random-access response. Control elements are identifiedwith reserved values in the LCID field, where the LCID value indicatesthe type of control information. Furthermore, the length field in thesub-header is removed for control elements with a fixed length.

The MAC multiplexing functionality is also responsible for handling ofmultiple component carriers in the case of carrier aggregation. Thebasic principle for carrier aggregation is independent processing of thecomponent carriers in the physical layer, including control signaling,scheduling and hybrid-ARQ retransmissions, while carrier aggregation isinvisible to RLC and PDCP. Carrier aggregation is therefore mainly seenin the MAC layer, where logical channels, including any MAC controlelements, are multiplexed to form one (two in the case of spatialmultiplexing) transport block(s) per component carrier with eachcomponent carrier having its own hybrid-ARQ entity.

Meanwhile, UEs that already have a valid grant obviously do not need torequest uplink resources. However, to allow the scheduler to determinethe amount of resources to grant to each terminal in future subframes,information about the buffer situation and the power availability isuseful, as discussed above. This information is provided to thescheduler as part of the uplink transmission through MAC controlelement. The LCID field in one of the MAC subheaders is set to areserved value indicating the presence of a buffer status report.

From a scheduling perspective, buffer information for each logicalchannel is beneficial, although this could result in a significantoverhead. Logical channels are therefore grouped into logical-channelgroups and the reporting is done per group. The buffer-size field in abuffer-status report indicates the amount of data available transmissionacross all logical channels in a logical-channel group.

FIG. 13A and FIG. 13B are examples for format of SL BSR MAC CE.

The Buffer Status Reporting (BSR) procedure is used to provide a servingeNB with information about the amount of data available for transmission(DAT) in the UL buffers of the UE. RRC may control BSR reporting byconfiguring the three timers periodicBSR-Timer and retxBSR-Timer andlogicalChannelSR-ProhibitTimer and by, for each logical channel,optionally signaling Logical Channel Group (LCG) which allocates thelogical channel to an LCG.

The sidelink Buffer Status reporting procedure is used to provide theserving eNB with information about the amount of sidelink data availablefor transmission in the SL buffers associated with the MAC entity. RRCcontrols BSR reporting for the sidelink by configuring the two timersperiodic-BSR-TimerSL and retx-BSR-TimerSL. Each sidelink logical channelbelongs to a ProSe Destination. Each sidelink logical channel isallocated to an LCG depending on the priority of the sidelink logicalchannel and the mapping between LCG ID and priority which is provided byupper layers in logicalChGroupInfoList. LCG is defined per ProSeDestination.

A sidelink Buffer Status Report (BSR) shall be triggered if any of thefollowing events occur: if the MAC entity has a configured SL-RNTI i) SLdata, for a sidelink logical channel of a ProSe Destination, becomesavailable for transmission in the RLC entity or in the PDCP entity andeither the data belongs to a sidelink logical channel with higherpriority than the priorities of the sidelink logical channels whichbelong to any LCG belonging to the same ProSe Destination and for whichdata is already available for transmission, or there is currently nodata available for transmission for any of the sidelink logical channelsbelonging to the same ProSe Destination, in which case the Sidelink BSRis referred below to as “Regular Sidelink BSR”, ii) UL resources areallocated and number of padding bits remaining after a Padding BSR hasbeen triggered is equal to or larger than the size of the Sidelink BSRMAC control element containing the buffer status for at least one LCG ofa ProSe Destination plus its subheader, in which case the Sidelink BSRis referred below to as “Padding Sidelink BSR”, iii) retx-BSR-TimerSLexpires and the MAC entity has data available for transmission for anyof the sidelink logical channels, in which case the Sidelink BSR isreferred below to as “Regular Sidelink BSR”, iv) periodic-BSR-TimerSLexpires, in which case the Sidelink BSR is referred below to as“Periodic Sidelink BSR”. Else, An SL-RNTI is configured by upper layersand SL data is available for transmission in the RLC entity or in thePDCP entity, in which case the Sidelink BSR is referred below to as“Regular Sidelink BSR”.

For Regular and Periodic Sidelink BSR, if the number of bits in the ULgrant is equal to or larger than the size of a Sidelink BSR containingbuffer status for all LCGs having data available for transmission plusits subheader, the MAC entity reports Sidelink BSR containing bufferstatus for all LCGs having data available for transmission. Else, theMAC entity reports Truncated Sidelink BSR containing buffer status foras many LCGs having data available for transmission as possible, takingthe number of bits in the UL grant into consideration.

If the Buffer Status reporting procedure determines that at least oneSidelink BSR has been triggered and not cancelled: if the MAC entity hasUL resources allocated for new transmission for this TTI and theallocated UL resources can accommodate a Sidelink BSR MAC controlelement plus its subheader as a result of logical channelprioritization, the MAC entity instructs the Multiplexing and Assemblyprocedure to generate the Sidelink BSR MAC control element(s), starts orrestarts periodic-BSR-TimerSL except when all the generated SidelinkBSRs are Truncated Sidelink BSRs, and starts or restartsretx-BSR-TimerSL.

Else if a Regular Sidelink BSR has been triggered, if an uplink grant isnot configured, a Scheduling Request shall be triggered.

A MAC PDU shall contain at most one Sidelink BSR MAC control element,even when multiple events trigger a Sidelink BSR by the time a SidelinkBSR can be transmitted in which case the Regular Sidelink BSR and thePeriodic Sidelink BSR shall have precedence over the padding SidelinkBSR.

The MAC entity shall restart retx-BSR-TimerSL upon reception of an SLgrant.

All triggered regular Sidelink BSRs shall be cancelled in case theremaining configured SL grant(s) valid for this SC Period canaccommodate all pending data available for transmission. All triggeredSidelink BSRs shall be cancelled in case the MAC entity has no dataavailable for transmission for any of the sidelink logical channels. Alltriggered Sidelink BSRs shall be cancelled when a Sidelink BSR (exceptfor Truncated Sidelink BSR) is included in a MAC PDU for transmission.All triggered Sidelink BSRs shall be cancelled, and retx-BSR-TimerSL andperiodic-BSR-TimerSL shall be stopped, when upper layers configureautonomous resource selection.

The MAC entity shall transmit at most one Regular/Periodic Sidelink BSRin a TTI. If the MAC entity is requested to transmit multiple MAC PDUsin a TTI, it may include a padding Sidelink BSR in any of the MAC PDUswhich do not contain a Regular/Periodic Sidelink BSR.

All Sidelink BSRs transmitted in a TTI always reflect the buffer statusafter all MAC PDUs have been built for this TTI. Each LCG shall reportat the most one buffer status value per TTI and this value shall bereported in all Sidelink BSRs reporting buffer status for this LCG.

FIG. 13A is an example for Sidelink BSR and Truncated Sidelink BSR MACcontrol element for even N, and FIG. 13B is an example for Sidelink BSRand Truncated Sidelink BSR MAC control element for odd N.

Sidelink BSR and Truncated Sidelink BSR MAC control elements consist ofone group index field, one LCG ID field and one corresponding BufferSize field per reported target group.

The Sidelink BSR MAC control elements are identified by MAC PDUsubheaders with LCIDs as specified in Table 1. They have variable sizes.

TABLE 1 Values of LCID for UL-SCH

Index 

LCID Values 

00000 

CCCH 

00001-01010 

Identity of the logical channel 

01011 

CCCH 

01100-10101 

Reserved 

10110 

Truncated Sidelink BSR 

10111 

Sidelink BSR 

11000 

Dual Connectivity Power

Headroom Report 

11001 

Extended Power Headroom Report 

11010 

Power Headroom Report 

11011 

C RNTI 

11100 

Truncated BSR 

11101 

Short BSR 

11110 

Long BSR 

11111 

Padding 

For each included group, the fields of the FIG. 13A and FIG. 13B aredefined as follows:

A field of “Group index” identifies the ProSe Destination. The length ofthis field is 4 bits. The value is set to the index of the destinationreported in destinationInfoList.

A field of “LCG ID” identifies the group of logical channel(s) whichbuffer status is being reported. The length of the field is 2 bits andit is set to “11”.

A field of “Buffer Size” identifies the total amount of data availableacross all logical channels of a ProSe Destination after all MAC PDUsfor the TTI have been built. The amount of data is indicated in numberof bytes. It shall include all data that is available for transmissionin the RLC layer and in the PDCP layer. The size of the RLC and MACheaders are not considered in the buffer size computation. The length ofthis field is 6 bits. The values taken by the Buffer Size field areshown in Table 2.

TABLE 2 Buffer size levels for BSR

Index 

Buffer Size (BS) value [bytes] 

 0 

BS = 0 

 1 

 0 < BS <= 10 

 2 

10 < BS <= 12 

 3 

12 < BS <= 14 

 4 

14 < BS <= 17 

 5 

17 < BS <= 19 

 6 

19 < BS <= 22 

 7 

22 < BS <= 26 

 8 

26 < BS <= 31 

 9 

31 < BS <= 36 

10 

36 < BS <= 42 

11 

42 < BS <= 49 

12 

49 < BS <= 57 

13 

57 < BS <= 67 

14 

67 < BS <= 78 

15 

78 < BS <= 91 

16 

 91 < BS <= 107 

17 

107 < BS <= 125 

18 

125 < BS <= 146 

19 

146 < BS <= 171 

20 

171 < BS <= 200 

21 

200 < BS <= 234 

22 

234 < BS <= 274 

23 

274 < BS <= 321 

24 

321 < BS <= 376 

25 

376 < BS <= 440 

26 

440 < BS <= 515 

27 

515 < BS <= 603 

28 

603 < BS <= 706 

29 

706 < BS <= 826 

30 

826 < BS <= 967 

31 

 967 < BS <= 1132 

32 

1132 < BS <= 1326 

33 

1326 < BS <= 1552 

34 

1552 < BS <= 1817 

35 

1817 < BS <= 2127 

36 

2127 < BS <= 2490 

37 

2490 < BS <= 2915 

38 

2915 < BS <= 3413 

39 

3413 < BS <= 3995 

40 

3995 < BS <= 4677 

41 

4677 < BS <= 5476 

42 

5476 < BS <= 6411 

43 

6411 < BS <= 7505 

44 

7505 < BS <= 8787 

45 

 8787 < BS <= 10287 

46 

10287 < BS <= 12043 

47 

12043 < BS <= 14099 

48 

14099 < BS <= 16507 

49 

16507 < BS <= 19325 

50 

19325 < BS <= 22624 

51 

22624 < BS <= 26487 

52 

26487 < BS <= 31009 

53 

31009 < BS <= 36304 

54 

36304 < BS <= 42502 

55 

42502 < BS <= 49759 

56 

49759 < BS <= 58255 

57 

58255 < BS <= 68201 

58 

68201 < BS <= 79846 

59 

79846 < BS <= 93479 

60 

 93479 < BS <= 109439 

61 

109439 < BS <= 128125 

62 

128125 < BS <= 150000 

63 

    BS <= 150000 

A field of “R” is a Reserved bit by setting to “0”.

For one to one communication, unicast addresses (i.e. Source UE ID andDestination UE ID) are set in SRC and DST fields respectively in MACheader. RAN2 makes an initial assumption that the ID remains 24 bits (16MSBs of destination UE ID is set in the DST field in MAC header and 8LSBs of destination UE ID are included in scheduling controlinformation). A new MAC PDU format version number indicates that unicastaddresses are set in SRC and DST fields.

The legacy SL BSR has Group Index field which identifies the ProSeDestination. The length of this field is 4 bits, and the value is set tothe index of the destination reported in destinationInfoList inSidelinkUEInformation message.

Then, a question comes, how the Group Index in SL BSR is mapped tounicast ID. This document addresses this issue.

FIG. 14 is a diagram for generating and transmitting a sidelink bufferstatus reporting in a D2D communication system according to embodimentsof the present invention,

First, it is expected that a new IE, e.g. unicast-destinationInfoList,would be included in the SidelinkUEInformation message to inform the eNBof the unicast ID to which the UE would send SL data.

The UE transmits information related to a first destination informationlist including at least one groupcast destination identifier (ID) and asecond destination information list including at least one unicastdestination ID via RRC message (S1401).

Preferably, the information related to a first destination informationlist and the second destination information is “destinationInfolist” inSidelinkUEInformation.

The information of “destinationInfoList” indicates the destination(s)for relay or non-relay related one-to-one or one-to-many sidelinkcommunication. For one-to-one sidelink communication the destination isidentified by the ProSe UE ID for unicast communication, while forone-to-many the destination it is identified by the ProSe Layer-2 GroupID as specified in TS 23.303.

The UE assigns values of destination index to groupcast destinations IDsin listing order in the first destination information list (S1403). Andthen remaining values of the destination index after setting to thegroupcast destinations IDs to unicast destinations IDs in listing orderin the second destination information list, sequentially (S1405).

Preferably, the UE is a non-relay UE. The relay UE relays SL data fromthe eNB to the Remote UE. The non-relay UE transmits SL data to a peerUE via sidelink, directly.

The UE generates and transmits a SL BSR MAC CE including at least onedestination index field identifying at least one destination, when SLBSR is triggered (S1407).

Preferably, one of the at least one destination index field have one toone correspondence to one of the assigned values of destination index.

Preferably, a total number of the groupcast destination IDs and theunicast destinations IDs is less than or equal to 16.

In the legacy, the Group Index values are mapped to groupcast IDs inlisting order in destinationInfoList. If the total number of groupcastID and unicast ID is less than or equal to 16, there are remainingvalues in Group Index after mapping to groupcast IDs, and thoseremaining values can be mapped to unicast IDs in listing order inunicast-destinationInfoList.

For example, if destinationInfoList contains {groupcast ID1, groupcastID2} and unicast-destinationInfoList contains {unicast ID1, unicast ID2,unicast ID3}, then the mapping between Group Index and groupcast/unicastIDs are as follows: i) Group Index 0=groupcast ID1, ii) Group Index1=groupcast ID2, iii) Group Index 2=unicast ID1, iv) Group Index3=unicast ID2, v) Group Index 4=unicast ID3.

Preferably, a size of the destination index field is 4-bits.

Preferably, the at least one unicast destination ID is identified by aLayer-2 ID for unicast communication, and the at least one groupcastdestination ID is identified by the ProSe Layer-2 Group ID.

If the total number of the groupcast destination IDs and the unicastdestinations IDs is more than 16, a new SL BSR should be introducedbecause there is no room for extension in legacy SL BSR format. As a newSL BSR is introduced, a new LCID value or R bit in R/R/E/LCID MACsubheader should be used to indicate the new SL BSR.

In this case, the mapping rule between Group Index and groupcast/unicastIDs are same as above mentioned.

The Group Index values are first mapped to groupcast IDs in listingorder in destinationInfoList, and then mapped to unicast IDs in listingorder in unicast-destinationInfoList. An example of new SL BSR format isshown in FIG. 15.

FIG. 16 is a diagram for generating and transmitting a sidelink bufferstatus reporting in a D2D communication system according to embodimentsof the present invention.

The UE transmits information related to a first destination informationlist including at least one groupcast destination identifier (ID) and asecond destination information list including at least one unicastdestination ID via RRC message (S1601).

Preferably, the information related to a first destination informationlist and the second destination information is “destinationInfolist” inSidelinkUEInformation.

The information of “destinationInfoList” indicates the destination(s)for relay or non-relay related one-to-one or one-to-many sidelinkcommunication. For one-to-one sidelink communication the destination isidentified by the ProSe UE ID for unicast communication, while forone-to-many the destination it is identified by the ProSe Layer-2 GroupID as specified in TS 23.303.

The UE assigns values of destination index for groupcast to groupcastdestinations IDs in listing order in the first destination informationlist and values of destination index for unicast to unicast destinationsIDs in listing order in the second destination information listindependently (1603).

The UE generates and transmits a SL BSR MAC CE including at least oneindex type indication indicating whether a corresponding destinationindex field refers to a unicast destination or a groupcast destination,when SL BSR is triggered (S1605).

Preferably, a total number of the groupcast destination IDs and theunicast destinations IDs is more than 16.

If a new SL BSR is introduced to extend the Group Index size, it ispossible to include Index Type indication in the new SL BSR. The IndexType indication indicates whether the Group Index refers to thegroupcast ID or unicast ID. The inclusion of Index Type indicator meansthat groupcast ID and unicast ID can be mapped to different Group Indexspace, and thus there is no reason to define a new mapping rule to mapthe Group Index values for both groupcast IDs and unicast IDs. Each typeof Group Index follows the legacy mapping rule, i.e. Group Index forgroupcast are mapped to groupcast IDs in listing order indestinationInfoList, and Group Index for unicast are mapped to unicastIDs in listing order in unicast-destinationInfoList.

Preferably, if an index type indication indicates that a destinationindex field refers a groupcast destination, a value of the destinationindex field is set to one of the values of destination index forgroupcast. And if an index type indication indicates that a destinationindex field refers a unicast destination, a value of the destinationindex field is set to one of the values of destination index forunicast.

For example, if destinationInfoList contains {groupcast ID1, groupcastID2} and unicast-destinationInfoList contains {unicast ID1, unicast ID2,unicast ID3}, then the mapping between Group Index and groupcast/unicastIDs are as follows: i) Index Type=groupcast, Group Index 0=groupcastID1, ii) Index Type=groupcast, Group Index 1=groupcast ID2, iii) IndexType=unicast, Group Index 0=unicast ID1, iv) Index Type=unicast, GroupIndex 1=unicast ID2, v) Index Type=unicast, Group Index 2=unicast ID3.

Preferably, a LCID field indicates that the SL BSR MAC CE includes theat least one index type indication.

Preferably, the at least one unicast destination ID is identified by aLayer-2 ID for unicast communication, and the at least one groupcastdestination ID is identified by the ProSe Layer-2 Group ID.

An example of new SL BSR format with Index Type indication is shown inFIG. 17.

Meanwhile, there are other options related to separate SL BSR forunicast.

If the size of group index is less than or equal to 16, our inventionsuggest an option A. This option means that the legacy SL BSR is usedfor groupcast, and a new SL BSR is used for unicast. The indication ofthe new SL BSR can be achieved by new LCID value or R bit in R/R/E/LCIDMAC subheader. The format of the new SL BSR is same as the legacy one.The difference from the legacy SL BSR is that the Group Index values inthe new SL BSR are mapped to unicast IDs rather than groupcast IDs, i.e.Group Index values are mapped to unicast IDs in listing order inunicast-destinationInfoList. If the size of group index is more than or16, our invention suggest an option B.

This option is similar to the option A, a new SL BSR is used for unicastwhile the legacy SL BSR is used for groupcast. However, the format ofthe new SL BSR should be different from the legacy one because the sizeof Group Index should be extended. The format in FIG. 15 can also be anexample of the new SL BSR format with Option B.

However, option A and option B are not good idea, because the separateSL BSR may require separate trigger/cancellation condition, separatetimer handling, and separate construction method. The logical channelprioritization procedure is also impacted due to introduction ofseparate SL BSR for unicast.

In Rel-12, RAN2 have already experienced complex situation due tointroduction of SL BSR. Lots of issues were identified in handling SLBSR together with Uu BSR, and RAN2 spent much time to resolve thoseissues. If we now introduce one more type of SL BSR, the situation wouldbecome more complex. Thus, we propose that separate SL BSR is notintroduced for unicast, and use only one SL BSR for both groupcast andunicast.

If 16 values are sufficient, the embodiment of FIG. 14 can be used, i.e.only the mapping rule is changed to cover both groupcast ID and unicastID.

If 16 values are not sufficient, a new SL BSR format needs to beintroduced as FIG. 16. The embodiment of FIG. 16 has a good pointbecause the Group Index for unicast is not impacted by addition/removalof groupcast ID.

However, we have to think about the impact when introducing a new SLBSR. Introducing a new SL BSR has big impacts on standardization, e.g.design of new format, modification of logical channel prioritization fornew MAC CE, handling of truncated SL BSR, etc. Moreover, indication of anew SL BSR also needs to be discussed considering that not many LCIDvalues are left and one of the R bit is already used for other purpose(i.e. L field extension in enhanced CA).

The embodiments of the present invention described herein below arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with an MS may be performed by the BS, or networknodes other than the BS. The term ‘eNB’ may be replaced with the term‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, forexample, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

While the above-described method has been described centering on anexample applied to the 3GPP LTE system, the present invention isapplicable to a variety of wireless communication systems in addition tothe 3GPP LTE system.

What is claimed is:
 1. A method for a user equipment (UE) operating in awireless communication system, the method comprising: transmittinginformation related to a first destination information list including atleast one groupcast destination identifier (ID) and a second destinationinformation list including at least one unicast destination ID;assigning values of destination index for groupcast to groupcastdestinations IDs using the first destination information list and valuesof destination index for unicast to unicast destinations IDs using thesecond destination information list; and generating and transmitting aSideLink Buffer Status Reporting (SL BSR) Medium Access Control (MAC)Control Element (CE) including at least one index type indicationindicating whether a corresponding destination index field refers to aunicast destination or a groupcast destination, when SL BSR istriggered.
 2. The method according to claim 1, wherein when the valuesof destination index for groupcast are assigned, the values ofdestination index for groupcast are assigned to groupcast destinationsIDs in listing order in the first destination information list.
 3. Themethod according to claim 1, wherein when the values of destinationindex for unicast are assigned, the values of destination index forunicast are assigned to unicast destinations IDs in listing order in thesecond destination information list.
 4. The method according to claim 1,wherein if an index type indication indicates that a destination indexfield refers a groupcast destination, a value of the destination indexfield is set to one of the values of destination index for groupcast. 5.The method according to claim 1, wherein if an index type indicationindicates that a destination index field refers a unicast destination, avalue of the destination index field is set to one of the values ofdestination index for unicast.
 6. The method according to claim 1,wherein a Logical Channel Identifier (LCID) field indicates that the SLBSR MAC CE includes the at least one index type indication.
 7. Themethod according to claim 1, wherein the at least one unicastdestination ID is identified by a Layer-2 ID for unicast communication,and the at least one groupcast destination ID is identified by the ProSeLayer-2 Group ID.
 8. The method according to claim 1, wherein a totalnumber of the groupcast destination IDs and the unicast destinations IDsis more than
 16. 9. A User Equipment (UE) for operating in a wirelesscommunication system, the UE comprising: a Radio Frequency (RF) module;and a processor operably coupled with the RF module and configured to:transmit information related to a first destination information listincluding at least one groupcast destination identifier (ID) and asecond destination information list including at least one unicastdestination ID, assign values of destination index for groupcast togroupcast destinations IDs using the first destination information listand values of destination index for unicast to unicast destinations IDsusing the second destination information list, and generate and transmita SideLink Buffer Status Reporting (SL BSR) Medium Access Control (MAC)Control Element (CE) including at least one index type indicationindicating whether a corresponding destination index field refers to aunicast destination or a groupcast destination, when SL BSR istriggered.
 10. The UE according to claim 9, wherein when the values ofdestination index for groupcast are assigned, the values of destinationindex for groupcast are assigned to groupcast destinations IDs inlisting order in the first destination information list.
 11. The UEaccording to claim 9, wherein when the values of destination index forunicast are assigned, the values of destination index for unicast areassigned to unicast destinations IDs in listing order in the seconddestination information list.
 12. The UE according to claim 9, whereinif an index type indication indicates that a destination index fieldrefers a groupcast destination, a value of the destination index fieldis set to one of the values of destination index for groupcast.
 13. TheUE according to claim 9, wherein if an index type indication indicatesthat a destination index field refers a unicast destination, a value ofthe destination index field is set to one of the values of destinationindex for unicast.
 14. The UE according to claim 9, wherein a LogicalChannel Identifier (LCID) field indicates that the SL BSR MAC CEincludes the at least one index type indication.
 15. The UE according toclaim 9, wherein the at least one unicast destination ID is identifiedby a Layer-2 ID for unicast communication, and the at least onegroupcast destination ID is identified by the ProSe Layer-2 Group ID.16. The UE according to claim 9, wherein a total number of the groupcastdestination IDs and the unicast destinations IDs is more than 16.